1. Field of the Invention
This invention relates in general to earth boring bits but in particular to improvements in their lubricant pressure compensators and relief means.
2. Description of the Prior Art
Earth boring bits of the rolling cutter type have sealed bearings and lubrication systems that include pressure compensation and relief means to minimize the pressure differential across the seals that separate the lubricant from the drilling mud in a bore hole.
A successful seal means is disclosed by Edward M. Galle in U.S. Pat. No. 3,397,928. A successful pressure compensation and relief means is disclosed by Stuart C. Millsapps, Jr., in U.S. Pat. No. 4,055,225. Other systems include the use of the original commercially successful pressure relief valve disclosed by Galle in U.S. Pat. No. 3,476,195 and the use of a pinhole or slit in a flexible compensator or diaphragm that permits liquid flow either into or from the compensator cavity, as disclosed by Schumacher in U.S. Pat. No. 3,847,234.
The failure of any element in the lubrication system of a bit eventually, but usually soon, concludes its useful life. Too often, a life determinative failure occurs in either the diaphragm or the relief means. Varying stresses caused by the lubricant pressure variations in a bit, along with increased temperatures downhole, accelerate compensator failure, especially those which include metal components bonded to rubber.